- Together, these results are consistent with the hypothesis that the pain and tenderness in FM may be due to tonically inactive DNIC analgesic systems. These results, however, do not specify causality and could also represent a mechanism in which DNIC is tonically activated in CMI in response to the widespread ongoing pain of the disease. These alternative mechanisms cannot be separated using conventional psychophysical tests. Performing the tests in the fMRI scanner will differentiate these mechanisms because in one case the DNIC system remains "OFF" in the patient populations, in the other case the DNIC system is constantly "ON." fMRI analysis of activity in brainstem regions (e.g., caudal medulla) implicated in intrinsic DNIC analgesia will provide evidence for tonic ON or OFF activity in these regions, and in addition further specify the neuroanatomical locus of this abnormal pain processing. The fMRI analysis will provide crucial evidence of whether FM results from a DNIC defect or whether the DNIC abnormality is simply one of the signs of the disease.